There are numerous machining methods for producing gearwheels and other rotationally-symmetric precision parts. The precision part is typically measured during or after the machining.
In order to be able to test the precision of the machining of a precision part after the machining, the precision part 11 can be removed from the machine tool and chucked in a special measuring system 10, for example, where it is scanned and measured using sensors 15, as indicated in FIG. 1. Numerically controlled measuring devices 10 are preferably used for this purpose. A rotationally-symmetric precision part 11 is typically chucked between a lower centering tip 13 and an upper centering tip 14 for the measurement. The lower centering tip 13 is seated on a turntable 13.1, which can be moved precisely into various angular positions by a drive. The precision part 11 is pressed against the lower centering tip 13 because of its intrinsic weight and the contact pressure which originates from the upper centering tip 14. The centering tip 13 has a rotational axis which runs coaxially to the first rotational axis A1. An arm 14.1 is preferably provided, which can be displaced vertically, as indicated by the double arrow 14.2. The upper centering means 14 is mounted within the arm 14.1 so that it can rotate easily around a vertical axis which is congruent with the rotational axis A1. The measuring device 10 comprises, as shown in FIG. 1, at least one sensor 15 for three-dimensional measurement (referred to as a 3-D scanning system) of the precision part 11 chucked in the measuring system 10. An arm 15.1 is preferably provided, which can be displaced vertically, as indicated by the double arrow 15.2. In addition, the sensor 15 can execute a feed movement, as indicated by the two double arrows 15.3 and 15.4 perpendicular to one another.
The published German patent application DE 10 2006 041 886 A1 concerns a robot-based system for the positioning of workpieces. A measuring device is employed in order to determine the actual position of the workpiece and the robot is caused to move the workpiece to adjust the position.
An apparatus for centering a workpiece in a lathe turning machine is disclosed in JP 06 039683 A. Four radially oriented actuators are positioned around a diskshaped workpiece. These actuators serve as position correcting means. One sensor is employed to determine whether the rotational axis of the workpiece is co-axially aligned with the rotation axis of the lathe. In case the workpiece is found to be not properly centered, the position correcting means are caused to correct the position of the workpiece.
Another apparatus for centering a cylindrical workpiece in a lathe turning machine is disclosed in U.S. Pat. No. 4,218,825. The cylindrical workpiece is mounted on a turn table. The positions of reference points on the periphery of the workpiece are determined and deviations are calculated using angular information. Press-members serve as position correcting means. These press-members apply a force to move the workpiece into a centered position.
The document WO 02/101792 discloses an alignment tool for aligning a robot blade which carries a workpiece. The respective system is designed in order to be able to determine the orientation of a workpiece.
The published German patent application DE 196 31 620 A1 discloses a grinding machine and means for determining the actual position of a gear wheel in such a machine. The determination of the position is carried out in order to use the data so obtained for the machining of the gear wheel. That is the data are transferred into the coordinate system of the machine and are used to perform a correction or do a compensation of machine movements in case of a misaligned gear wheel.
A system for quantitatively and qualitatively determining the spatial position of two objects is disclosed in the published German patent application DE 10 2006 023 926 A1. The system comprises a laser transmitter which emits a light beam which is split into several beams. Several row or line sensors are employed for determining the positions where the respective beams impinge.
The document EP 0 377 796 A2 discloses another approach with three sensors to align a cylindrical workpiece which is horizontally oriented.
Experience has shown that with large and heavy precision parts, such a construction having a lower centering tip 13 and an upper centering tip 14 is not capable of being able to precisely orient the precision part 11 before the measurement.
The need is increasingly expressed for being able to measure precision parts having large diameter and high weight. In addition, an important requirement for measurements of this type is that they are performed very precisely, on the one hand, but also as rapidly as possible, on the other hand.
The typical measuring systems do not meet such requirements. Even small deviations, which result because of imprecise placement of the precision part in the measurement structure, result in large measurement inaccuracies. This is also true for the placement of large workpieces in machine tools. The introduction (setup) of a large and heavy workpiece is also often problematic and time-consuming here.
It is an object of the invention to provide a device and a corresponding method in order to allow the rapid and reliable placement of larger and/or heavier precision parts.
In particular, the object is to be achieved by the present invention of improving a measuring device, e.g., a numerically controlled measuring device (CNC measuring device) so that it is capable of rapid complete measurement of a large and/or heavy precision part, such as a gearwheel, and the measuring device nonetheless has a simple and operationally-reliable construction.
In particular, the object is to be achieved by the present invention of improving a machining device, such as a numerically controlled machine tool (CNC gear cutting center), so that it is capable of rapid gear cutting of a large and/or heavy precision part, such as a gearwheel, and nonetheless has a simple and operationally-reliable construction.
The object is achieved by a device and by a method of the present invention.
The subjects of claims form advantageous embodiments of the device and method according to the invention.